Field of the Invention
This invention relates to a method for forming a metal oxide coating layer on a catalyst support. More particularly, this invention relates to a method for forming a metal oxide catalyst carrier on the surface of the catalyst support, wherein the catalyst carrier is produced by forming a metal-containing precipitate on the surface of the catalyst support and calcinating the precipitate.
Description of the Related Art
A catalyst reactor has been used in devices for posttreatment of the exhaust gases from vehicles, and in various chemical processes such as hydrogen production and desulfurization. The catalyst reactor is constructed to carry catalysts such as nickel, ruthenium, platinum, palladium, rhodium, etc. in a catalyst carrier formed on the surface of a catalyst support.
The catalyst support is usually made of a ceramic or metal, and configured to form a passage of reactants flowing through the catalyst reactor. The catalyst support may be variously fabricated in a form of felt, mat, mesh, foam, foil, monolith, or pin. The catalyst carrier is formed by coating a ceramic such as alumina, boehmite, silica, titania, etc. on the surface of the catalyst support, and functions as a carrier of the catalysts.
Since the catalyst reactor is normally used at a high temperature, the catalyst carrier may be detached from the catalyst support due to the difference of thermal expansion coefficients between the support and the carrier, which results in deteriorating durability and efficiency of the catalyst reactor. Therefore, it matters to increase the binding force between the support and the carrier. Further, it matters to increase the specific surface area of the carrier for enhancing a possibility of dispersedly carrying the catalysts and contacting the catalysts with the reactants, which results in improved catalytic activity and conversion efficiency.
Korean Patent No. 10-1019234 (Patent Literature 1) discloses a method of preparing a metal support in a compact reformer for increasing a binding force between a catalyst carrier and a catalyst support, and a specific surface area of the carrier. The method comprises the steps of electrochemical surface treatment for a metal catalyst support to form an amorphous metal oxide layer on the metal support by controlling an applied voltage and an electrolyte concentration, and heat treatment for the electrochemically surface-treated metal support in a heating furnace under an oxidation atmosphere to crystallize the amorphous metal oxide layer formed on the metal support or to form a metal oxide layer containing a specific metal component. Patent Literature 1 employs the metal oxide on the metal support, or another carrier layer coated on the metal oxide as a catalyst carrier.
FIG. 1 is schematic views showing catalyst carriers produced by Patent Literature 1, in which a catalyst is loaded in the carriers.
Referring to FIG. 1, FIG. 1(a) is a schematic view which shows a metal oxide 20 formed on a catalyst support 10 after electrochemical surface treatment and heat treatment. The metal oxide 20 is used as a catalyst carrier and the catalyst 30 is directly loaded on the metal oxide 20.
We found that the binding force between the catalyst 30 and the metal oxide 20, and catalytic activity were not high when the catalyst 30 was directly loaded on the metal oxide 20 formed on the catalyst support after electrochemical surface treatment and heat treatment, as shown in FIG. 1(a).
FIG. 1(b) is a schematic view which shows the metal oxide 20 formed on the catalyst support 10 after electrochemical surface treatment and heat treatment, and another carrier layer 40 coated on the metal oxide 20. Such construction is intended to solve the problem that the binding force between the catalyst 30 and the metal oxide 20 and catalytic activity deteriorate when the catalyst 30 is directly loaded on the metal oxide 20. FIG. 1(b) shows that the catalyst 30 is loaded on the carrier layer 40.
As shown in FIG. 1(b), when the catalyst 30 is loaded on the carrier layer 40 formed on the metal oxide 20, the binding force between the carrier layer 40 and the catalyst 30 is improved and, therefore, the catalytic activity is increased.
However, the surface of the carrier layer 40 is relatively rough and, therefore, its specific surface area is not high, because Patent Literature 1 forms the carrier layer 40 on the metal oxide 20 by spraying, impregnation, washcoating, etc. Further, we found that the carrier layer 40 was occasionally detached from the catalyst support 10, because the carrier layer 40 and the catalyst support 10 were physically bonded.